The endless power transmission belt wound onto a pulley includes, for example, V belts (e.g., wrapped belts, raw edge belts, raw edge cogged belts), V-ribbed belts, flat belts, and the like which transmit power by the frictional force at contact surface with the pulley, and toothed belts which transmit power by engaging with teeth of the pulley. In many of these power transmission belts, in order to transmit power from a driving pulley to a driven pulley and to reinforce a rubber-made belt body, a tension member extending in the circumferential direction is embedded in the belt and at the same time, working surface of the belt coming into contact or engage with the pulley is covered with a cover fabric such as canvas. In some cases, the whole circumference of the belt body including the working surface is covered with a cover fabric. In the toothed belt, tooth parts engaging with teeth of the pulley are provided at predetermined intervals in the circumferential direction of a belt body, and a tension member is embedded in the back part lying in the circumferential direction on the back side of the belt body.
The toothed belts are often used in a belt drive mechanism for driving an automotive engine camshaft, injection pump, oil pump, water pump and the like. In association with the recent increase in engine power output, the load on the belt is increased and at the same time, the usage environment for the belt becomes harsh due to, for example, the increase in ambient temperature involved in downsizing of the engine room. In addition, also in a large two-wheeled vehicle, shift from a chain or shaft drive to a belt drive using a toothed belt is recently proceeding. Therefore, toothed belts used for vehicles are required to be more enhanced in durability. Furthermore, it is required also for toothed belts used in general industrial machines to extend the replacement cycle in high-load applications such as injection molding machine and to enhance the durability.
The damage mode of the toothed belts is roughly grouped into a belt break by the occurrence of cracks due to flexural fatigue of the tension member or insufficient heat resistance of the rubber and a tooth crack attributable to wear of the cover fabric (tooth fabric) covering the tooth part. As the measure against the belt break due to flexural fatigue of the tension member, it has been proposed to properly set the occupancy of the tension member in the belt width direction and to set the twist factor defined by the number of twists and size (fineness) of the tension member (see, for example, Patent Document 1). As the measure against the belt break due to insufficient heat resistance of the rubber, it has been proposed to use an unsaturated carboxylic acid metal salt-containing hydrogenated acrylonitrile-butadiene rubber as a matrix rubber and to add a heat-resistant short fiber or the like thereto (see, for example, Patent Document 2). As the measure against the tooth crack attributable to wear of the tooth fabric, it has been proposed to use a fluorine-based fiber having a low friction coefficient as a weft yarn of the tooth fabric (see, for example, Patent Document 3). For the warp and weft yarns of the tooth fabric, a multifilament yarn obtained by converging a plurality of filaments is generally used.
The cover fabric covering at least a part of the rubber-made belt body is generally subjected to an adhesion treatment such as resin treatment with isocyanate or the like, resorcin-formaldehyde-latex (RFL) treatment, and rubber cement treatment, in order to enhance the adherability to the rubber. By performing such an adhesion treatment, the adhesion treating solution is impregnated into and attached to the surface of the yarn forming the cover fabric or the space between filaments constituting the yarn, and the attached adhesive component is fixed after drying.
Patent Document 1: JP-A-2009-257344
Patent Document 2: JP-A-2008-291205
Patent Document 3: JP-A-2005-240862